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<h1><a href="https://archiveofourown.org/works/25891120">The Sibling Thing</a> by <a class='authorlink' href='https://archiveofourown.org/users/onamaewa/pseuds/onamaewa'>onamaewa</a></h1>

<table class="full">

<tr><td><b>Category:</b></td><td>Undertale (Video Game)</td></tr>

<tr><td><b>Genre:</b></td><td>Incest, No beta we die like humans, Other, PWP, implied past CSA</td></tr>

<tr><td><b>Language:</b></td><td>English</td></tr>

<tr><td><b>Status:</b></td><td>Completed</td></tr>

<tr><td><b>Published:</b></td><td>2020-08-14</td></tr>

<tr><td><b>Updated:</b></td><td>2020-08-14</td></tr>

<tr><td><b>Packaged:</b></td><td>2021-05-05 11:06:53</td></tr>

<tr><td><b>Rating:</b></td><td>Explicit</td></tr>

<tr><td><b>Warnings:</b></td><td>Creator Chose Not To Use Archive Warnings, Rape/Non-Con, Underage</td></tr>

<tr><td><b>Chapters:</b></td><td>1</td></tr>

<tr><td><b>Words:</b></td><td>2,383</td></tr>

<tr><td><b>Publisher:</b></td><td>archiveofourown.org</td></tr>

<tr><td><b>Story URL:</b></td><td>https://archiveofourown.org/works/25891120</td></tr>

<tr><td><b>Author URL:</b></td><td>https://archiveofourown.org/users/onamaewa/pseuds/onamaewa</td></tr>

<tr><td><b>Summary:</b></td><td><div class="userstuff">
              <p>They had to keep it a secret; that was the rules. Some grown-ups, like Asriel's Mom and Dad, wouldn't understand.</p>
            </div></td></tr>

<tr><td><b>Relationships:</b></td><td>Chara/Asriel Dreemurr</td></tr>

<tr><td><b>Comments:</b></td><td>1</td></tr>

<tr><td><b>Kudos:</b></td><td>18</td></tr>

</table>

<a name="section0001"><h2>The Sibling Thing</h2></a>
<div class="story"><div class="fff_chapter_notes fff_head_notes"><b>Author's Note:</b><blockquote class="userstuff">
      <p>This was originally named "Regret", because the author regretted writing it. Into the poorly-written sin bin it goes.</p>
    </blockquote></div><div class="userstuff module">
    
    <p>Chara was very quiet when Mom and Dad made the announcement. Asriel had thought they would be excited, becoming a part of the family, but they just seemed... uncertain. Their smile didn't reach their eyes, and his parents either missed it entirely (Dad) or ignored it (Mom).</p><p>Maybe they're nervous? he wondered, watching Chara's face intently out of the corners of his eyes. Chara didn't like to talk much about their life on the surface, and never about their family. Asriel wasn't even sure they had one.</p><p>Maybe that was why. If they'd never had a family before, it could make sense to be a little scared or uncertain. Chara often disliked new and unexpected things, after all. He had learned that from experience.</p><p>They had really liked him, though. That was a rare exception, he'd guessed.</p><p>After a minute or so of contemplation from Chara, they nodded, the forced smile never leaving their face. They told Mom and Dad that if they wanted to adopt them, they could. Mom smiled warmly at them, and Dad moved to give them a hug for a moment before remembering they didn't like being touched very much, least of all unexpectedly.</p><p>To everyone's surprise, Chara didn't shy away, at least not clearly. Instead, they turned towards Dad and held out their arms, as if waiting. Dad hugged them hesitantly, like a wild animal that might flee at any moment, and Asriel could see them tense slightly when his arms touched theirs, but they leaned into the hug in a stiff movement that seemed genuine.</p><p>They turned their head to look at Asriel, asking how old he was, anyway? Asriel supposed they had never asked before, in the last few weeks they spent in the house, recovering from the fall.</p><p>"Nine," he said, trying to smile. It was hard, when they seemed so unhappy and trying to hide it. Their face fell a little more at his answer.</p><p>They were eleven, they told him. That would make him their younger brother.</p><p>He couldn't tell why this made it worse, but he didn't ask, either. If they didn't want to talk about, they didn't have to tell him.</p><p> </p><p> </p><p>Dad was out for the day, and Mom had gone to get groceries, so the house stayed quiet except for their wandering around. Chara beckoned him to the spare bedroom, and locked the door once he was inside.</p><p>Asriel looked around. "What are we doing?"</p><p>Chara pointed to the closet, then opened the door and jerked their head in a 'get in' motion. Asriel followed them, and they shut the door.</p><p>The closed closet was big enough they both stood roughly an arm's length apart, and it was dark, enough to mask Chara's face. Asriel couldn't say what they were thinking. Their hands were warm through his shirt as they touched his side, almost tentative at first, before pressing themself against him. Despite being the elder sibling, they were still a little smaller than him.</p><p>"What was it you wanted to do?" he whispered, sensing a need for secrecy.</p><p>They told him it was the sibling thing. The one older siblings did with littler ones. The one older brothers did with younger ones. He probably didn't know about it, because he was an only child.</p><p>"You already said that. What's the thing?" he asked.</p><p>A secret, they explained.Their secret. He already knew that too. As his eyes adjusted a little to the darkness, he could piece together the shape of a frown. Chara continued, facing him now, staring straight at him in the faint light from under the door.</p><p>Chara asked if he was ready. Asriel nodded. "Can you show me now?"</p><p>Chara agreed, and told him the first step: to take off his pants. That was a little strange, but it wasn't like he really needed them, so he pulled them down around his ankles. Chara stared as his front and legs, squinting a little and tilting their head -- surprised. Was something wrong?</p><p>"Chara, are you..."</p><p>They shook their head and smiled at him. The dimness made it hard to define the shape of their eyes. He couldn't say how honest the smile was, but it felt too wide and sharp, the corners all wrong.</p><p>Chara looked up and down, eyes glinting but dull. They asked him to turn around.</p><p>"Why?" he asked, curious. They didn't answer, but instead pulled a hanger from the bar above and slid it into the door hinge. They told him again to turn around.</p><p>Asriel balked at the command, a little anxious now. Something didn't seem right. "Why?", he asked again.</p><p>They paused for a moment, then said they wanted to look at his tail. Asriel could find no fault in that, he supposed, so he turned around, still a little uncertain.</p><p>He heard Chara take a deep breath. They muttered something that sounded like an apology, but they seemed... resigned. Their curious fingers brushed against his tail, petting it. Asriel laughed a little, nervously.</p><p>Softly, they asked him not to panic. This was special. Just for the two of them.</p><p>They pushed up closer to him, movements halting at first and then smoother, forceful. He let out a startled shriek of protest when they shoved him against the closet wall, pinning their bodies side by side, closer than Chara had ever wanted or tolerated in the past.</p><p>"Ch-chara? What are you--?"</p><p>He cut off the question with a yelp as something touched under his tail, worming its way in, cold despite the warmth radiating from them both. It didn't belong. He flailed and tried to turn back to face his sibling, but they didn't back off, only gentling their touch. It would get better, they explained. It always felt a little weird at first, but he would like it. He was supposed to.</p><p>This wasn't right. Asriel tried to untangle himself from their grip, but they moved in front of the door and reached around to touch between his legs. He squirmed and tried to pull away-- that spot wasn't anything special, but Chara didn't seem themself, and none of this was --</p><p>As he took a half-step, it felt like Chara panicked. They pleaded him to stay.</p><p>"I don't like this, and I'm not staying!" he insisted, dragging himself another step.</p><p>They repeated themself. He would like this. He would enjoy it, he just had to wait. Didn't he trust them?</p><p>As he tried another step, their eyes widened, then narrowed in knowledge. If he was going to be a weenie about it, they'd just do it. They tackled him-- they couldn't manage a running start inside the closet, but they still slammed him against the wall with full weight, and he saw stars.</p><p>The pinpricks were almost pretty. What came next wasn't.</p><p>He was pressed flat face-first in the corner of the closet. Chara must have taken their pants off, too, because he could feel their bare legs against the back of his. He couldn't feel his own pants around his ankles, but he could feel cloth underneath him. They were probably on the floor.</p><p>Something warm pressed against his back, and there was an uncomfortable cold pressure somewhere he didn't want to think about. Chara was much too close, and when they grabbed his arms, still pressing themself tight to his torso, and turned him around to face them, their cheeks were flushed and hot.</p><p>They were smiling. He didn't have to look to see it didn't reach their eyes. They mumbled something under their breath like an incantation, and hooked their legs around his chest, knocking him to the ground. His head hit the wall, and the world turned to sparks again.</p><p>They were on top of him, hands around his muzzle. Their shirt was gone as well, and something dangled in front of his face. It looked like a finger, or skin, but he couldn't name it. Chara hadn't stopped mumbling, quiet and furious and indistinct, and clawed at his muzzle, trying to force it open. They pressed the thing against his neck and chin, and he squirmed as hard as he could.</p><p>"STOP, please, Chara--" he gasped, and they grabbed the opportunity, trying to pry his jaws apart and slide the thing in. His jaw was strong enough to snap shut before they could, though, and they shrieked in rage and pain -- he must have scraped it. Was it really that sensitive?</p><p>As they pulled off of him, Asriel tried to get to his feet, but they were already back on top of him, enraged. Something struck him across the stomach, cold sharp metal, and he just recognized the shape in Chara's hands as a coat-hanger,</p><p>The wire made a whistling sound when it swung fast enough. Twice, at least, and not counting whatever might have missed as they rolled him over again, and he cried out. His belly felt numb and cold, like it had been beaten with an ice bag, and he winced when it landed on the floor.</p><p>He could feel Chara's sweat against his fur, and their rage was palpable. They bit his ear, and he sobbed in fear and hurt and confusion. Why were they doing this? What was happening? He hadn't had time to think, and he barely could now.</p><p>They were touching him down there again, forcing a hole open he hadn't remembered being there, one that felt too sensitive, ticklish even. Tears streaked down his face as they told him to take it like a man. The words didn't sound anything like their own.</p><p>This was what little siblings got from bigger ones. It was a special thing, a good thing, and he was supposed to appreciate it, not cry like a baby, they hissed at him, forcing their hand against him so hard it hurt, and he whimpered, bruised and terrified.</p><p>They pressed something else into him back there, with he could only guess at now that their arms had slipped around his crotch, squeezing him together from both sides. They began to push on him in a growing rhythm, in and out, and it hurt like something scraping and aching, like a knife in his insides.</p><p>"CHARA, PLEASE--"</p><p>They wadded up a shirt from the floor and forced it into his mouth when he called out, and elbowed him in the back of the neck, driving his snout into the carpet. The rhythm continued, more intense, until he wailed through the gag with each impact against him that hurt his hips against the floor. Something was pushing, moving inside of him. It was strange and still too much, and--</p><p>Something slipped farther in, and he froze at the sudden burst of pleasure. The happiness of eating chocolate cake, the beauty of sunlight, the sleepy comfort of a lazy hour in bed in the morning -- it was almost like that, for a split second, before he remembered where he was and what was happening.</p><p>It came again as they shoved against him, in waves. He didn't want this either, but they weren't lying after all, were they? It felt nice, and he hated it, even more because it was the kind of nice he couldn't even enjoy. Like a sweet taste that burns your tongue, or your favorite song played over an awful conversation. Chara's gift wasn't very good like this, and even though he was scared and angry, a tiny part of him wondered if it could have been better if he hadn't said no.</p><p>Then they grunted and climbed off of him, and it was over.</p><p>Asriel lay on the floor and kept crying, softly, while Chara panted with effort. He didn't get up for a while, just lying there, trying not to think about anything that would make him start crying harder again, like the crybaby Chara muttered that he was.</p><p>Eventually, Chara moved toward him again. Asriel didn't get out a whole word through his tears, only flinched away and curled against the corner.</p><p>They had been a crybaby too, the first time, they told him. They cried and cried, but they were good and didn't tell.</p><p>Asriel curled up a little tighter. "Why not? Why didn't you tell?"</p><p>Because he's their brother. They're siblings, and siblings don't tell on each other like that. Not about their secrets. Not about this.</p><p>"But wasn't it bad?" He sniffled, and tried to make sense of the picture. Chara, who was shy and quiet. Chara, who loved him, maybe more than they did anyone else in the family, more than Mom or Dad. Chara, who--</p><p>Who--</p><p>Chara knelt in silence next to him. They never met his eyes, but now, they didn't even face him.</p><p>Remember when you tried Dad's coffee? they asked. Their voice felt calmer now. Steadier, but with his eyes adjusted to the closet, Asriel could see their hands balled up in fists against their bare legs.</p><p>"Yeah," he said, after a moment of watching them. It was hard to tell, but they were shaking. "It was awful."</p><p>Chara nodded. The sibling thing was like that, they explained. It seemed bad at first, but it would be worth it, if Asriel got used to it. That's how it was before. If you learned to ignore the bitterness for the best parts, eventually it wasn't so bad at all. Grown-ups did it all the time, too, because they were older and already learned to like it. It was like practice, but secret, and just for siblings.</p><p>"I didn't like it, though," Asriel protested, but he felt like he was lying. There had been that feeling at the end, after all. He just was too scared and hurt to enjoy it.</p><p>He still had to promise not to tell, though. Even if they didn't do it again. They had to keep it a secret; that was the rules. Some grown-ups, like Asriel's Mom and Dad, wouldn't understand.</p><p>"I..." Asriel's words fell quiet behind his teeth.</p><p>Please promise, Chara pleaded. Promise you won't tell.</p><p>He could see their eyes now, even if they were averted, and the way they bit their lip. Their face was wet, and their hands still shook.</p><p>Asriel took a deep breath, slow and steady.</p><p>"... Okay."</p><p>He exhaled. Braced himself.</p><p>"I promise."</p>
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